What is the recommended dose of amoxicillin (amoxicillin) for a typical adult patient with a common bacterial infection?

Recommended Amoxicillin Dosing for Adults with Common Bacterial Infections

For most common bacterial infections in adults, the standard amoxicillin dose is 500 mg three times daily (every 8 hours) or 875 mg twice daily (every 12 hours) for 7-10 days, taken at the start of meals to minimize gastrointestinal side effects. 1

Standard Adult Dosing by Infection Severity

Mild to Moderate Infections

• 500 mg every 8 hours (three times daily) for ear/nose/throat, skin/skin structure, and genitourinary tract infections 1
• Alternative: 500 mg every 12 hours for less severe presentations 1
• Duration: minimum 48-72 hours beyond symptom resolution 1

Severe Infections or Resistant Pathogens

• 875 mg every 12 hours (twice daily) for more severe ear/nose/throat, skin, and genitourinary infections 1
• Alternative: 500 mg every 8 hours if twice-daily dosing is not tolerated 1

Lower Respiratory Tract Infections

• 875 mg every 12 hours or 500 mg every 8 hours regardless of severity 1
• This higher dosing is necessary for adequate lung tissue penetration 1

High-Dose Regimens for Resistant Organisms

When treating infections with suspected resistant bacteria (particularly penicillin-resistant Streptococcus pneumoniae), amoxicillin 4 grams daily is recommended. 2

High-dose amoxicillin is indicated when patients have: 2

• Recent antibiotic use within 4-6 weeks
• Failed previous antibiotic therapy
• Moderate to severe infection
• Age over 65 years
• Significant comorbidities
• Immunocompromised status
• Exposure to daycare settings or smokers

The pharmacokinetic advantage of high-dose amoxicillin is that serum levels increase linearly with dose—gastrointestinal absorption is not a limiting factor, and adverse effects between standard and high doses are negligible. 2

Specific Clinical Scenarios

Acute Bacterial Rhinosinusitis

• First-line for mild disease without recent antibiotic use: 1.5-4 g/day divided into 2-3 doses 2
• Duration: 5-7 days (as effective as 10 days for uncomplicated cases) 3
• Consider amoxicillin-clavulanate instead if risk factors present 2

Streptococcal Pharyngitis

• Standard dose: 500 mg twice daily for 10 days 4
• Alternative once-daily regimen: 1000 mg once daily for 10 days (for patients ≥40 kg) 5
• Minimum 10 days required to prevent acute rheumatic fever, regardless of clinical improvement 1

The once-daily regimen has been validated in large trials showing non-inferiority to twice-daily dosing, with comparable bacteriologic eradication rates (80-85%) and improved compliance. 5, 6

Group A Streptococcal Carrier Eradication

• 500 mg three times daily for 10 days when treating healthcare workers or chronic carriers with transmission risk 2
• Penicillin alone achieves only 80% eradication; consider clindamycin if initial treatment fails 2

Critical Dosing Considerations

Administration Timing

• Always take at the start of a meal to minimize gastrointestinal intolerance 1
• This is particularly important for higher doses

Treatment Duration

• Continue for minimum 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1
• 10 days minimum for any Streptococcus pyogenes infection to prevent rheumatic fever 1
• Some infections require several weeks of therapy with months of follow-up 1

Renal Impairment

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours 1
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours 1
• Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and after dialysis 1
• Do NOT use 875 mg dose if GFR <30 mL/min 1

Common Pitfalls to Avoid

Never substitute two 250 mg tablets for one 500 mg tablet when using amoxicillin-clavulanate formulations, as this results in excessive clavulanate dosing and increased diarrhea risk. 4

For lower respiratory tract infections, standard doses (500 mg three times daily) may be insufficient for bacterial pathogens. 7 The evidence shows amoxicillin provides minimal benefit in viral LRTI but may reduce illness deterioration when both bacterial and viral pathogens are present, supporting the use of adequate dosing when bacterial infection is suspected. 7

Amoxicillin is intrinsically less active against β-lactamase-producing organisms (Haemophilus influenzae, Moraxella catarrhalis), so consider amoxicillin-clavulanate for infections where these pathogens are likely. 2